Stars  To understand the life cycle of stars Thursday, June 23, 2016

The Universe  What is the origin of the Universe?  A lot of evidence and information has been gathered about the universe, and observations have led to the development of the Big Bang theory  The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point  This began to enlarge rapidly in a hot explosion, and it is still expanding today – this Big Bang happened about 15 billion years ago

Big Bang  Since all galaxies appear to be moving apart at a rapid rate, this suggests there was an initial explosion – the Big Bang  All the matter in the Universe must have been compressed into a very small space, which exploded and expanded around 15 billion years ago (and is continuing today)  The age of the Universe can be estimated by the current rate of expansion (although accuracy is a problem as it is difficult to identify if this expansion has been slowing)  The rate of expansion is important as this will decide the future of the Universe (gravity slows the expansion down…)

Future Of The Universe  The fate of the Universe depends on how fast the expansion is, as well as the total mass within it (tricky to identify as our observations of how much mass are much lower than our predictions – most mass is probably contained within black holes / dark matter etc… which become difficult to identify)  Depending on the rate of expansion and mass of the Universe two possibilities exist (excluding the steady state theory): -  The Big Crunch – if there is a critical mass compared to the expansion then the Universe will eventually stop expanding and begin contracting (which could be cyclic…)  Constant expansion – if the mass is below the critical point then the Universe will expand forever

Stars  Stars go through many stages in their lives  Protostar – star formation initially from clouds of dust and gas where gravity makes the dust and gas spiral together  Main sequence star – a stable period where the force of gravity is balanced by an equal outward pressure caused by nuclear fusion  Red giant – star runs out of hydrogen and eventually swells then cools, finishing ‘life’ as a white dwarf  Red super giant – very large stars run out of hydrogen and swell and then explode in a supernova, finishing ‘life’ as a neutron star or black hole

Stars